The present invention relates to an electric actuator that provides an angular reciprocating drive for electric hand tools.
Angular reciprocating motions are often required in electric hand tools, such as electric toothbrushes in particular. In an electric toothbrush, the reciprocating motion is conventionally and invariably provided by means of an electric motor driving a cam or crank system that translates rotation into reciprocation. There are shortcomings. The cam/crank system represents additional components that have an adverse effect on production cost and mechanical reliability. The indirect transmission of force results in loss of power. Moreover, hygiene is compromised as the cam/crank system introduces inner spaces and corners or the like where stain can build up.
The invention seeks to mitigate or at least alleviate such problems by providing an electric actuator of a novel type.
According to the invention, there is provided an electric actuator for providing an angular reciprocating drive, comprising a casing, a stator housed in the casing, and an armature extending co-axially through the stator. The stator has an annular arrangement of poles and a coil for energization by an alternating current to magnetise the poles in opposite polarities as between adjacent poles. The armature has a shaft supported by the casing for angular movement and a plurality of permanent magnets mounted fast on and around the shaft. The magnets have proximal sides as between adjacent magnets of opposite polarities, wherein upon repeated reversals of said alternating current the magnets interact magnetically with the poles to cause the shaft to oscillate thereby providing said drive.
Preferably, the magnets are located at equiangular positions around the shaft.
Preferably, each magnet is elongate and extends in substantially the same direction as the shaft.
More preferably, each magnet has a flat surface, and the shaft has a corresponding flat surface against which the magnet lies with its flat surface.
Further more preferably, the magnets are located equiangularly around a section of the shaft, the section having a substantially polygonal cross-section that provides a plurality of flat surfaces positioning the respective magnets.
It is preferred that each magnet has opposite ends and extends substantially parallel to the shaft, and the magnets are secured on the shaft by a pair of mounting members surrounding respective opposite ends of the magnets.
In a preferred embodiment, the poles are divided into two groups each of alternating poles, and the stator includes a pair of ferromagnetic annual members located at opposite ends thereof, each member being connected to a respective group of alternating poles for magnetisation in the same polarity.
More preferably, the poles as between the two groups are shifted in opposite directions for connection with the corresponding annual members.
In a specific construction, the stator includes a spool, around which the coil is wound and inside which the poles are positioned.
More specifically, the spool includes a pair of annual flanges at opposite ends thereof, between which the coil is wound.
More specifically, the spool includes a plurality of grooves on an inner surface thereof, each groove extending axially relative to the spool and locating a respective pole.
It is preferred that the poles and the magnets are arranged in respective equiangular manners, and the number of poles is the same as or an integral multiple of the number of the magnets.
In a preferred embodiment, the armature includes a torsion spring biassing the shaft into a neutral angular position relative to the casing, across which neutral position the shaft is to oscillate.
More preferably, the poles and the magnets are arranged in such a manner that each magnet is positioned symmetrically between a corresponding pair of poles when the shaft is in the neutral position.
More preferably, the spring comprises a coil spring disposed co-axially on the shaft.
More preferably, the spring has a first end engaged with a fixed member on the shaft and a second end engaged with an end cap of the casing.
Further more preferably, the fixed member comprises an eccentric weight mounted fast on the shaft.
It is preferred that the armature includes an eccentric weight mounted fast on the shaft.
It is further preferred that the eccentric weight has a main body extending on a transverse plane of and partially round the shaft.
The invention also provides an electric hand tool incorporating the aforesaid electric actuator, including a body housing the actuator and an implement connectable to an output end of the shaft for driving thereby to reciprocate for operation.
As an example, the electric hand tool is an electric toothbrush, in that the body comprises a handle and the implement comprises a brush head.